Fuel cells, such as proton exchange membrane (PEM) fuel cells and solid oxide fuel cells (SOFC), are arguably the most energy efficient and clean energy generation systems. These fuel cells require hydrogen as the fuel. One method for producing hydrogen is by catalytic reforming of natural gas with liquefied petroleum gas (LPG), i.e., commercial propane and butane, used to a lesser extent. These fuels are often the fuels of choice for hydrogen because of their relative abundance and availability of supply infrastructure. Such fuels are often dosed with sulfur odorants, such as thiols and sulfides, for handling during transportation and utilization. Residual H2S may remain in these fuels (˜5-10 ppm). It is desirable to remove these sulfur compounds before feeding to the catalytic reformers, in part, because they may poison both the catalysts in the reformers and the catalysts in the fuel cells.
The concentrations of sulfur in pipeline natural gas and LPG are typically around 10 ppm or higher. Raw natural gas from wellhead contains a significant amount of sulfur in the form of H2S. The concentration varies widely from ppm levels up to 5%. The acceptable sulfur levels for reformers and fuel cells are well below 1 ppm, (for example, <0.01 ppm).
It is desirable that the H2S be removed to a level below 10 ppm before distribution in pipelines. Current technologies used to remove H2S include solvent extraction using amine solutions or adsorption at ambient temperatures using fixed bed adsorbers (e.g., activated carbon or zinc oxide (ZnO)). These sorbents generally do not have high sulfur selectivity and high sulfur capacity; and furthermore, they are used as disposable sorbents because they are not regenerable.